Field emission display and methods of forming a field emission display

ABSTRACT

A field emission device and method of forming a field emission device are provided in accordance with the present invention. The field emission device is comprised of a substrate ( 12 ) having a deformation temperature that is less than about six hundred and fifty degrees Celsius and a nano-supported catalyst ( 22 ) formed on the substrate ( 12 ) that has active catalytic particles that are less than about five hundred nanometers. The field emission device is also comprised of a nanotube ( 24 ) that is catalytically formed in situ on the nano-supported catalyst ( 22 ), which has a diameter that is less than about twenty nanometers.

FIELD OF THE INVENTION

[0001] The present invention generally relates to a field emissiondevice, and more particularly to a field emission display and methods offorming a field emission display (FED).

BACKGROUND OF THE INVENTION

[0002] A nanotube, and more specifically a carbon nanotube, is known tobe useful for providing electron emission in field emission devices,such as cold cathodes that are used in a field emission display. The useof a carbon nanotube as an electron emitter has reduced the cost of afield emission device, including the cost of a field emission display.The reduction in cost of the field emission display has been obtainedwith the carbon nanotube replacing other electron emitters (e.g., aSpindt tip), which generally have higher fabrication costs as comparedto a carbon nanotube based electron emitter.

[0003] The manufacturing costs for a field emission display that uses acarbon nanotube can be further reduced if the carbon nanotube is grownon the field emission substrate from a catalytic surface using chemicalvapor deposition or other film deposition techniques. Nanotube growthcan be done as a subsequent deposition process preventing thedegradation of the electron emitter properties by other deviceprocessing techniques or steps (e.g., wet processes). To further reducecosts for a field emission display, it is also desirable to constructthe field emission substrate from materials such as borosilicate glassor sodalime glass. However, borosilicate glass and sodalime glass cannotgenerally tolerate temperatures above about sixty hundred and fiftydegrees Celsius (650° C.) and the tolerance of borosilicate glass andsodalime glass is further reduced if the borosilicate glass or sodalimeglass is subjected to temperatures above about sixty hundred and fiftydegrees Celsius (650° C.) for an extended period or forces are appliedto the borosilicate glass or sodalime glass at about such temperatures.To even further reduce costs, it is desirable to use low switchingvoltage driver electronics in a field emission display. However, a fieldemission display using carbon nanotubes generally have a higherswitching voltage than what can be provided by these low switchingvoltage driver electronics.

[0004] In view of the foregoing, it is desirable to provide low gatevoltage field emission display that uses low switching voltage driverelectronics, carbon nanotubes as electron emitters and a field emissionsubstrate that has a deformation temperature below about six hundred andfifty degrees Celsius (650° C.). Furthermore, additional desirablefeatures will become apparent to one skilled in the art from thedrawings, foregoing background of the invention and following detaileddescription of a preferred exemplary embodiment, and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The present invention will hereinafter be described inconjunction with the appended drawing figures, wherein like numeralsdenote like elements, and:

[0006] FIGS. 1-11 are sectional, top plan and isometric viewsillustrating the method of forming cathodes according to a preferredexemplary embodiment of the present invention;

[0007]FIG. 12 is a top isometric view illustrating an array of theportion of the cathodes formed according to the preferred exemplaryembodiment of the present invention;

[0008]FIG. 13 is an enlarged view of a portion of FIG. 12; and

[0009]FIG. 14 is a field emission display constructed according to apreferred exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0010] The following detailed description of preferred embodiments ismerely exemplary in nature and is not intended to limit the invention orthe application and uses of the invention. Furthermore, there is nointention to be bound by any theory presented in the precedingbackground of the invention or the following detailed description ofpreferred embodiments.

[0011] FIGS. 1-11 illustrate a method of forming a cathode that can beused to construct a field emission display (FED) according to apreferred exemplary embodiment of the present invention. Referring toFIG. 1, the formation of the cathode begins with providing a fieldemission substrate 12. The field emission substrate 12 has a deformationtemperature below about six hundred and fifty degrees Celsius (650° C.)and is preferably borosilicate glass or sodalime glass, however anynumber of materials can be used for the field emission substrate 12according to the present invention. For example, the field emissionsubstrate 12 can be other glasses, silicon, carbon, ceramics, metals,and composite materials. If the field emission substrate 12 is asemiconductor material and control electronics has been integrated intothe display, an insulating layer or multiple insulating layers arepreferable to reduce capacitance within the FED.

[0012] A conductive layer 14 is deposited with any number of depositiontechniques on the field emission substrate 12 and patterned by standardphotolithographic methods. Generally, the conductive layer 14 includes ametal, such as titanium, tungsten, chromium, molybdenum, copper, or thelike, that will adhere to the field emission substrate 12 and supportthe formation of a nano-supported catalyst layer 22 as will besubsequently discussed in this detailed description of the drawings. Ascan be appreciated by one of ordinary skill in the art, the thickness 15of the conductive layer 14 is a function of the desired application. Ascan be seen in FIG. 2, which provides a top plan-view of FIG. 1, theconductive layer 14 is preferably formed into an elongated strip with anexpanded portion defining an emitter area. The elongated strip providesexternal electrical connections to the emitters (i.e., nanotubes formedin the emitter area).

[0013] Referring to FIG. 3, a bleed layer 15 can be optionally depositedover the conductive layer 14 and extended outwardly on the surface ofthe field emission substrate 12 beyond the conductive layer 14 and intocontact with a metal gate 86 as subsequently described and illustratedwith reference to FIG. 9. The bleed layer 15 is preferably formed of amaterial having a resistance that is preferably greater thanapproximately 1×10¹¹ ohms, such as tantalum nitride (TaN), chromiumoxy-nitride (CrOxNy, where x=y equals 1) or the like, to allow chargeaccumulated during operation to bleed off so as to minimize anundesirable surface potential. Additional information on bleed layerscan be found in U.S Pat. No. 5,760,535, entitled “Field EmissionDevice,” issued Jun. 2, 1998, which is hereby incorporated by reference.

[0014] The thickness 16 of the bleed layer 15 is preferably less thanabout one hundred (100) angstroms to about eight hundred (800) angstromsin order to minimize the affect on the lateral flow of current from theconductive layer 14. Moreover, the relatively high resistance of thematerial forming the bleed layer 15 provides minimal current flowbetween the emitters (i.e., nanotubes 24) in the emitter area and therespective gate within the cathode. In order to maintain simplicity andclarity in this detailed description of the drawings, the bleed layer 15is considered to be a portion or sub layer of the conductive layer 14 ifthe bleed layer 15 is present.

[0015] Referring to FIG. 4, a sacrificial layer 42 is deposited so as todefine an emitter well 20. One or more of the dimensions (i.e., diameter19, depth 21 etc.) of the emitter well 20 can be adjusted for theparticular application. In this detailed description of the drawings,the emitter well 20 has a diameter 19 of about forty (40) microns and adepth 21 of about twelve (12) microns. The sacrificial layer 42 ispreferably formed of photo-resist, but could be silicon-on-glass (SOG),a polyimide (Pl), a Q-pac, or the like. The material used for thesacrificial layer 42 is preferably selected such that the deposition,patterning, selective removal and cleaning processes associated with thesacrificial layer 42 during the formation of the emitter well 20 doesnot substantially remove or operably harm the conductive layer 14 and/orthe bleed layer 15.

[0016] Referring to FIG. 5, the nano-supported catalyst layer 22 isformed within the emitter well 20 illustrated in FIG. 4. In onepreferred embodiment, the nano-supported catalyst layer 22 is formedwith a method that begins with immersing the emitter well 20 illustratedin FIG. 4 in a solvent having a first metal salt and a second metalsalt. Any number of soluble metal salts can be used for the first metalsalt and the second metal salt as long as the first metal salt and thesecond metal salt react to form an insoluble metal, metal hydroxide,metal oxide or the like.

[0017] For example, the first metal salt can be aluminum nitrate,magnesium nitrate, calcium nitrate or combination thereof, and thesecond metal salt can be a metal nitrate or sulfate containing iron,nickel, cobalt, ruthenium, rhodium, palladium, rhenium, osmium, iridium,platinum, or a combination thereof. The first and second metal salts areat least partially dissolved in any number of solvents, including, butnot limited to, water, alcohol or a combination of water and alcohol(e.g., methanol, ethanol, and isopropyl alcohol). Additional compoundssuch as particles, surfactants, etc. can also be incorporated into thesolvent.

[0018] The immersion of the emitter well 20 illustrated in FIG. 4 intothe solvent having the first metal salt and the second metal salt can beaccomplished with numerous immersion techniques, including, but notlimited to, spin immersion, spray immersion, dip coating immersion, inkjet spraying followed by electrolysis or the like. Once the emitter wellis immersed into the solvent having the first metal salt and the secondmetal salt, a bias voltage is applied to the emitter well such that thenano-supported catalyst layer 22 is at least partially formed of thefirst metal and the second metal salt within the emitter well. Theapplication of the bias voltage is preferably applied with a biasingsource connected to the emitter well and a counter electrode of thebiasing source immersed in the solvent.

[0019] Alternatively, the nano-supported catalyst layer 22 can be formedby a second method, which begins with immersing the emitter well 20illustrated in FIG. 4 into a first solvent containing a first metalsalt. While the emitter well is immersed in the solvent containing thefirst metal salt, a bias voltage is applied from a counter electrode tothe emitter well such that the nano-supported catalyst layer 22 is atleast partly formed with the first metal salt. The emitter well with thepartial formation of the nano-supported catalyst layer 22 is removedfrom the first solvent containing the first metal salt, and immersedinto a second solvent containing a second metal salt. A bias voltage isapplied from a counter electrode to the emitter well such that thenano-supported catalyst layer 22 is partially formed with the secondmetal salt.

[0020] The second method for formation of the nano-supported catalystlayer 22 can use numerous materials, combinations of materials,solvents, metal salts, and metal salt concentrations in the solventsincluding the materials, combinations of materials, solvents, metalsalts, and metal salt concentrations in the solvent that were discussedabove with reference to the first method for formation of thenano-supported catalyst layer 22. For specific examples of the firstmethod and the second method for formation of the nano-supportedcatalyst layer 22, see Appendix 1. However, the examples set forth inAppendix 1 should not be construed as limiting embodiments of thepresent invention.

[0021] Unlike other conventional catalysts formed by electro-deposition,which generally have active catalytic particles with a dimension that isgreater than about one micron (1 μm) (i.e., diameter, width, length, ordepth), the nano-supported catalyst layer 22 formed according to the twopreviously described methods has active catalytic particles derived fromthe second metal salt (e.g., iron, nickel, cobalt, ruthenium, rhodium,palladium, rhenium, osmium, iridium, or platinum, or a combinationthereof) with a dimension that is about one-tenth of a nanometer (0.1nm) to about five hundred nanometers (500 nm). According to the presentinvention, the dimension of the active catalytic particle is preferablyless than fifty nanometers (50 nm), more preferably less than tennanometers (10 nm), even more preferably less than three nanometers (3nm), and most preferably less than one nanometer (1 nm), and supportedby the metal oxide derived from the first metal salt (e.g., the alumina,magnesium oxide, calcium oxide).

[0022] Altering the composition ratio between the second metal salt andthe remaining materials deposited to form the nano-supported catalystcan control the density of the active catalytic particles. Thenano-support provided by the metal oxide support maintains thenano-scale dimensions of the active catalytic particles through theuseful temperature of the catalytic process including the chemicalreaction process subsequently described in this detailed description ofthe drawings for growing nanotubes and prevents the active catalyticparticles from coalescing during such a catalytic process. Thisnano-support renders the particle size relatively independent of thethickness of the nano-supported catalyst layer 22 and temperature cycle.Furthermore, the metal oxide support can minimize diffusion of poisonsto the nano-supported catalyst layer 22 and can enhance chemicalreactivity. Due to the nano-supported structure, the nano-supportedcatalyst layer 22 has a high surface area and a high surface area tovolume ratio.

[0023] The nano-supported catalyst layer can also be formed according toa third method of the present invention. Referring to FIG. 6, the methodbegins with substantially the same or the same steps as previouslydescribed in this detailed description of the drawings. Morespecifically, the method begins with providing a field emissionsubstrate 12 and depositing and patterning a conductive layer 14 ontothe field emission substrate 12. However, the third method of thepresent invention also includes the deposition of at least two metallicelements to form a mixed metal alloy layer.

[0024] The deposition of the two metallic elements to form the mixedmetal alloy layer 23 can be achieved in any number of conventionaltechniques such as co-evaporation, co-sputtering, electro-deposition,laser ablation, or arc evaporation. The mixed metal alloy layer 23 ispreferably comprised at least two metallic elements that are generallydispersed uniformly. The first metallic element is preferably an activecatalytic metallic element. The second metallic element is preferably astructural metallic element that maintains the nano-scale dimensions ofthe nano-supported catalyst layer through the useful temperature of thecatalytic process (e.g., about five hundred degrees Celsius (500° C.) toabout one thousand degrees Celsius (1,000° C.) for hot filament chemicalvapor deposition (HFCVD)), and assists in preventing the activecatalytic metallic element from coalescing during such process.

[0025] It is preferred that the structural metallic element be a metaloxide. The active catalytic metallic element and the structuralcatalytic metallic element preferably have different electrochemicalselectivity thereby permitting the selective dissolution of thestructural metallic element during a subsequent etching process.Examples of a suitable active catalytic metallic element includetitanium, vanadium, chromium, manganese, copper, zirconium, niobium,molybdenum, silver, hafnium, tantalum, tungsten, rhenium, gold; andpreferably, ruthenium, rhodium, palladium, osmium, iridium, platinum;and more preferably iron, cobalt, nickel, or a combination thereof.Examples of a suitable structural metallic element include, withoutlimitation, silicon, magnesium, and preferably aluminum. Theconcentration or composition of the active catalytic metallic elementand the structural metallic element is controlled by the depositionconditions of each of the metallic elements such as electricaldischarge, partial pressure, temperature, and evaporation rate.

[0026] The composition of mixed metal alloy layer 23 influences thefinal structure and determines the activity of the nano-supportedcatalyst for cracking the hydrocarbon gas (e.g., methane) during HFCVD.The preferred composition of layer contains at least fifty percent (50%)of the active catalytic metallic element. The thickness 25 of the mixedmetal alloy layer 23 is a function of the desired application for thenano-supported catalyst layer. In some catalytic applications, thethickness 25 of the mixed metal alloy layer 23 can reach a few microns.However, for growing carbon nanotubes to be used in the FED, thenano-supported catalyst layer preferably has a thickness that is lessthan about one micron, more preferably less than about two hundrednanometers (200 nm), even more preferably less than one hundred andfifty nanometers (150 nm), and most preferably less than about onehundred nanometers (100 nm).

[0027] In a preferred exemplary embodiment, the deposition of the activecatalytic metallic element and the structural metallic element isachieved by co-evaporation. The co-evaporation process begins with theintroduction of the substrate into a vacuum environment. The vacuumenvironment is preferably less than about 1×10⁻⁶ Torr and can be createdwith any number of devices, including, but not limited, to a vacuumchamber. The active catalytic metallic element and the structuralmetallic element are co-evaporated to form the mixed metal alloy layer.The coevaporation of the active catalytic metallic element and thestructural metallic element can be performed using any number ofconventional apparatuses and methods.

[0028] In another preferred exemplary embodiment of the presentinvention, an additional element can be deposited to promote bettercatalytic activity of the nano-supported catalyst layer. Morespecifically, the additional element is deposited with the activecatalytic metallic element and the structural metallic element to formthe mixed metal alloy layer. Examples of a suitable additional elementinclude, without limitation, calcium, tantalum, hafnium, and zirconium.

[0029] After the formation of the mixed metal alloy layer 23, the firstsacrificial layer 42 is deposited to define each of the emitter wells asillustrated in FIG. 4. After the first sacrificial layer has beendeposited and patterned to define the emitter wells as illustrated inFIG. 4, the mixed metal alloy layer 23 is etched so that it remainsprimarily on the emitter wells (i.e., the electrodes). Once the mixedmetal alloy layer 23 is etched so that it remains primarily on theemitter wells, the method continues with the removal of the firstsacrificial layer.

[0030] Continuing with reference to FIG. 6, after the removal of thefirst sacrificial layer, the remaining mixed metal alloy layer 23 isetched to at least partially remove and selectively oxidize thestructural metallic element to form the nano-supported catalyst layer22. The etchant preferably targets the structural metallic elementhaving the electrochemically active element of the mixed metal alloylayer 23. Any number of dry or wet etch techniques can be used to etchthe mixed metal alloy layer 23 and the etchant, etchant concentrationand etch time are preferably selected to provide the partial removal andselective ioxidization of the structural metallic element. The etchingcan be achieved by immersing (e.g., spinning, spraying, dip coating,etc.) the mixed metal alloy layer 23 in an etching solution, preferablyfor approximately thirty (30) seconds to approximately forty (40)minutes, more preferably for approximately five (5) minutes toapproximately fifteen (15) minutes. Examples of suitable etchingsolution include, without limitation, NH₄OH, an alkali metal hydroxide(e.g., NaOH, KOH), and an acid (e.g., nitric acid, hydrochloric acid).

[0031] The partial removal and selective oxidation of the structuralmetallic element by the etchant is created by a kinetic rougheningtransition. This roughening transition results from a competitionbetween a roughening process (i.e., removal of the structural metallicelement) and a smoothing process (i.e., surface diffusion, volumediffusion, or dissolution/re-deposition). For the mixed metal alloylayer 23 below a critical alloying composition (e.g., containing atleast fifty percent (50%) of the active catalytic metallic element), thestructural metallic element is removed from the first few surface atomicsu-blayers of mixed metal alloy layer 23 resulting in an enrichment ofthe active catalytic metallic element in the sub-layers and the slowingof the dissolution process. Above a critical alloying composition, thedissolution rate of the structural metallic element is great enough todevelop a nano-porous support structure following the predefinedinterconnected channels of the structural metallic element within themixed metal alloy layer 23, the structural metallic element compositionis approximately greater than the percolation threshold. The dissolutionprocess continues to follow these pathways as the smoothing processresults in the coarsening of the three-dimensional structure in anattempt to minimize the overall surface energy. The coarsening allowsfor further penetration of the electrolyte into the mixed metal alloylayer 23.

[0032] Referring to FIG. 7, the nano-supported catalyst layer 22resulting from the etching of the mixed metal alloy layer has a porous(or sponge like) sub-layer 230 in electrical contact with a mixed metalalloy sub-layer 232. The porous sub-layer 230 is comprised of dispersedactive catalytic metallic element particles 222 (e.g., about one millionnano-particles per cm² to about ten billion nano-particles per cm )supported by a metal oxide structure 228 derived from the structuralmetallic element and filled with nano-pores 234 and tunnel structures(not shown) that are interconnected and random in direction. The poroussub-layer 230 is formed as the etching chemically drives the activecatalytic metallic element atoms to aggregate into clusters by a phaseseparation process at the solid-electrolyte interface, and increased thesurface area to volume ratio of mixed metal alloy layer. Substantiallyunaffected by the etching, the composition of mixed metal alloysub-layer 232 is substantially the same or the same as the mixed metalalloy layer.

[0033] Unlike other conventional catalysts which generally have activecatalytic metallic element particles that are greater than approximatelyone micron (1 μm), the nano-supported catalyst layer 22 resulting fromthe etching of the mixed metal alloy layer has active catalytic metallicelement particles 222 that are about one-tenth of a nanometer (0.1 nm)to about five hundred nanometers (500 nm), preferably less than aboutfifty nanometers (50 nm), more preferably less than about ten nanometers(10 nm), even more preferably less than about seven nanometers (7 nm),and most preferably less than three nanometers (3 nm). The nano-pores234 are generally irregular in shape and size. The size and distributionof the nano-pores 234 are dependent upon the electrolyte composition andconcentration, composition of the mixed metal alloy layer, etchantconcentration and the etching rate and period.

[0034] The nano-support provided by the metal oxide structure maintainsthe nano-scale dimensions of the active catalytic metallic elementparticles 222 through the useful temperature of the catalytic processincluding the chemical process that can be used for growing nanotubes(e.g., HFCVD) subsequently discussed in this detailed description of thedrawings and prevents the active catalytic metallic element particles222 from coalescing during such process. The nano-support renders theparticle size of the active catalytic metallic element 222 relativelyindependent of the thickness and temperature cycle of the nano-supportedcatalyst layer 22. Furthermore, the metal oxide structure can preventdiffusion of contaminants to the nano-supported catalyst layer 22 andcan improve the chemical reactivity. Due to its nano-supported porousstructure, nano-supported catalyst layer 22 resulting from the etchingof the mixed metal alloy layer has a relatively high surface area tovolume ratio, preferably greater than about fifty meter square per gram(50 m²/g), more preferably greater than about one hundred square pergram (100 m²/g), and most preferably greater than one hundred and fiftymeter square per gram (150 m²/g). After etching the mixed metal alloylayer 220, the nano-supported catalyst layer 22 is preferably driedaccording to the present invention. The drying process can beaccomplished with any conventional method. For example, the dryingprocess can be airflow over the nano-supported catalyst layer 22. For aspecific example of the formation of the nano-supported catalyst layer22 with the method of the third preferred embodiment of the presentinvention, see Appendix 1. However, this example set forth in Appendix 1should not be construed as limiting embodiments of the presentinvention. For example, see Example V of appendix 1 for a method ofnanotube preparation other than the first, second and third embodimentsof nanotube preparation previously described in this detaileddescription of the drawings.

[0035] Referring to FIG. 8, once the nano-supported catalyst layer 22has been formed within the emitter well 20 (see FIG. 4) with one of thepreviously described methods of the present invention, a secondsacrificial layer 72 is deposited and patterned so as to substantiallysurround the emitter well 20. The second sacrificial layer 72 is formedwith a depth and width that defines a gate separation from the emitterwell 20, as will be subsequently described in more detail. The secondsacrificial layer 72 is preferably formed of photo-resist to provideease in removal, but could be Silicon-On-Glass (SOG), polyimide (P1),Q-pac or the like. The material forming the second sacrificial layer 72is preferably configured to provide protection for the nano-supportedcatalyst layer 22 during deposition, patterning, etching or otherwiseremoving and cleaning and preferably minimize removal of the conductivelayer 14 and/or the bleed layer 15.

[0036] After the second sacrificial layer 72 is formed, a gate seedlayer 16 is deposited on the surface of the second sacrificial layer 72.Generally, the gate seed layer 16 is deposited with any number ofprocesses, such as evaporation, ceramic printing, or the like, toproduce a layer with a thickness that is greater than approximately onehalf (0.5) a micron and less than approximately two (2) microns. Thegate seed layer 16 can include titanium, tungsten, or chromium and alsoinclude copper to improve electrical conduction during subsequentelectroplating activities. The second sacrificial layer 72 is preferablyformed with generally rounded corners such that the gate seed layer 16can be evaporated onto the surface of the second sacrificial layer 72with substantial uniformity over the surface. If the sides of secondsacrificial layer 72 are too steep, breaks in the gate seed layer 16 canform and later plating applications may not form a substantially uniformlayer.

[0037] Referring to FIG. 9, a mask is formed on the gate seed layer 16to define a gate opening 82 and gate edges 84. In this preferredexemplary embodiment of the present invention, a layer of photo-resistis applied across the majority and preferably substantially all or theentire structure and then patterned and removed to leave only a portiondefining the gate opening 82 and the gate edges 84. However, is shouldbe understood that that other mask materials may be used, such asoxides, nitrides and the like.

[0038] With the mask in place, a gate layer 18 is plated onto theexposed surface of the gate seed layer 16. The gate layer 18 can be anynumber of conductive materials, such as copper. The material of the gatelayer 18 is preferably electroplated to form a gate or dome shape overthe structure with a thickness that is preferably in a range ofapproximately five (5) microns to approximately fifteen (15) microns.However, the thickness may vary depending on the desired application.The gate layer 18 combines with gate seed layer 16 to form asubstantially continuous gate 86. It will be understood, however, thatother deposition methods, such as vacuum deposition, thermal spray, etc.could be used in accordance with the present invention with otherconductive materials or metals.

[0039] When the cathodes are preferably fabricated into an array, thephoto-resist defining the gate edges 84 separates the electroplatedmaterial into multiple strips formed in a parallel and spaced-apartrelationship that are generally perpendicular to the strips formed inthe conductive layer 14. In this preferred embodiment, both the stripsformed in the conductive layer 14 and the substantially continuous gate86 are preferably separated by a distance that is greater than about ten(10) microns. This separation reduces row to column capacitance,probability of shorting and leakage paths between conductors, andprovides a vacuum dielectric, which will substantially reducedegradation due to electron bombardment.

[0040] Once the deposition of the gate layer 18 is completed, the maskis removed and the gate seed layer 16 is etched to form a gate opening82 through the substantially continuous gate 86. The gate seed layer 16can be a material that differs from gate layer 18 (e.g., titanium andcopper, respectively) so that it can be selectively etched or a portionof gate layer 18 may be allowed to etch. Also, portions of gate seedlayer 16 that are present between adjacent strips are preferably removedso that an electrical separation is provided between adjacent strips.

[0041] Referring to FIG. 10, the sacrificial layer 72 is removed toleave the gate 86 suspended over the emitter well 20. Upon removal ofthe sacrificial layer 72, the structure 90 shown in FIG. 10 isintroduced into a vacuum chamber where nanotubes 24, preferably carbonnanotubes, are grown on the surface of the nano-supported catalyst layer22 with a chemical reaction process such as a catalytic decomposition,pyrolysis, or chemical vapor deposition (CVD), and preferably hotfilament chemical vapor deposition (HFCVD). The techniques required forconducting these processes are known in the art.

[0042] As can be appreciated by one of ordinary skill in the art, thenanotube growth temperature of the substrate during the chemicalreaction process is a function of the substrate. For example, thenanotube growth temperature of a substrate of borosilicate glass ispreferably less than about six hundred and fifty degrees Celsius (650°C.), more preferably less than about six hundred degrees Celsius (600°C.), even more preferably less than about five hundred and fifty degreesCelsius (550° C.), and most preferably less than about five hundreddegrees Celsius (500° C.). As one of ordinary skilled in the art canappreciate, the nanotube growth temperature of other suitable substratesmay be higher than about six hundred and fifty degrees Celsius (650°C.).

[0043] As previously indicated in this detailed description of thedrawings, a HFCVD process is preferably used to grow carbon nanotubes 24on the nano-supported catalyst layer 22. The preferred HFCVD processbegins with the introduction of the structure 90 into a CVD growthchamber. A refractory metal filament (e.g., tungsten, platinum, rhenium,tantalum) is heated to a temperature above about nineteen hundreddegrees Celsius (1900° C.) in a vacuum or as molecular hydrogen isflowed over the refractory metal filament. Carbon containing gases suchas methane, acetylene, and xylene can also be flowed over the filamentto provide a carbon source for the nanotube growth.

[0044] More specifically, the structure 90 is placed into a thermallyconducting substrate holder (e.g., graphite) that is placed in apredefined location with respect to the hot filament (e.g., below thehot filament). The substrate holder can be a heater or it can bethermally connected to a heater. This configuration of the structure 90and the hot filament allows the temperature of the substrate (i.e., thenanotube growth temperature) to be independently controlled from the hotfilament temperature. During the growth of at least one carbon nanotubeand more preferably multiple carbon nanotubes 24 on the nano-supportedcatalyst layer 22 of the structure 90, the distance between the hotfilament and the field emission substrate 12 of the structure 90 is alsocontrolled to provide a temperature of the substrate (i.e., the nanotubegrowth temperature). For example, a distance of about one-half to abouttwo centimeters (about 0.5 cm to about 2 cm) between the hot filamentand the substrate 12 is provided for a nanotube growth (or substrate)temperature ranging from about three hundred and fifty degrees Celsius(350° C.) to about six hundred degrees Celsius (600° C.).

[0045] Once the desired nanotube growth temperature is provided on thefield emission substrate 12, a carbon source is introduced into the CVDgrowth chamber. Any hydrocarbon or carbon-compound (e.g., methane,carbon monoxide, etc.) can be used as the carbon source. For example, agas mixture of hydrogen (H₂) and methane (CH₄) can be used as thehydrocarbon source, with a flow rate of one hundred (100) standard cubiccentimeters per minute (sccm) for hydrogen and forty (40) sccm formethane. The methane is diluted by the hydrogen and thermallydisassociated and activated with the hot filament. The ratio of themethane to hydrogen is preferably maintained with the range ofapproximately twenty percent (20%) to approximately forty percent (40%)and the pressure of the CVD growth chamber is maintained at about twenty(20) to about fifty (50) Torr. The substantially simultaneous productionof atomic hydrogen during hydrocarbon pyrolysis enhances the depositionof the carbon nanotubes 24. Referring to FIG. 11, the formation of thenanotubes 24 is terminated when their tips reach the level of the gateaperture, which also completes the formation of the cathode.

[0046] Referring to FIG. 11 and as previously described in this detaileddescription of the drawings, the sacrificial layer 72 shown in FIG. 8 isformed with a depth and width that defines a gate separation from theemitter well 20. While some scaling is possible (e.g., changes in anodeoperating potential may include changes in emitter-gate spacing, etc.),the sacrificial layer 72 shown in FIG. 8 is formed with a height (H)from the emitter well 20 and a gate opening width (W). In a specificexample, the height (H) 81 can be approximately twelve (12) microns andthe width (W) 83 can be approximately twenty (20) microns. Generally, ithas been found that the thickness and height (H) of the gate 86 and thewidth (W) of the gate opening 82 are related to device performance andpreferably are proportionally maintained in accordance with the presentinvention. Also, the height (H) is configured for a vacuum space fromthe nanotubes 24 or the field emission substrate 12 that provides adesired dielectric strength by way of a vacuum gap.

[0047] With the assistance of the nano-supported catalyst layer 22, thenanotubes 24 are selectively and sparsely grown with a micro-pattern(i.e., sub-pixel or quantum dots). The nanotubes 24 are preferablysingle wall nanotubes or multi-walled nanotubes having a substantiallyuniform structure. The nanotubes 24 formed according to the presentinvention preferably have a diameter less than about twenty nanometers(20 nm), more preferably less than about ten nanometers (10 nm), andmost preferably less than about three nanometers (3 nm). In addition,the nanotubes 24 formed according to the present invention preferablyhave an aspect ratio, defined as height of the nanotube to the width ofthe nanotube, that is greater than about one hundred and forty (140),but less than about four thousand and five hundred (4,500), morepreferably greater than about one thousand (1,000), and most preferablygreater than about one thousand (1,000) but less than aboutthree-thousand and five hundred (3,500) with a substantiallyperpendicular orientation with respect to the surface of the substrate12. The nanotubes 24 also preferably have a significant dispersion inthat the spacing between the nanotubes 24 is between about twentynanometers (20 nm) to about two thousand nanometers (2,000 nm). A topplan view and an isometric view of a portion of an array of cathodes areillustrated in FIGS. 12 and an enlarged view of FIG. 12 is provided inFIG. 13. As can be seen in FIGS. 12 and 13, spacer mounting pads 92 areillustrated that are formed between adjacent rows of gates 86 to assistin maintaining a relatively fixed relationship between the anodes 13 andthe gates 86.

[0048] Referring to FIG. 14, the formation of a FED, having cathodesformed according to the present invention preferably continues with theformation of anodes 13 in a spaced relation from the gates 86. Theanodes 13 are formed by providing a substrate 30 upon which is depositeda transparent conductive layer 32 such as indium tin oxide (ITO). Thesubstrate 30 can be the same material or similar material as the fieldemission substrate 12. Multiple cathodoluminescent deposits 36 areformed on the transparent conductive layer 32 in alignment with the gateopening 82 in the gates 86. The anodes 13 are preferably spacedapproximately two hundred and fifty (250) microns to five thousand(5,000) microns from the substrate 12. The formation of the FED 10 iscompleted when the field emission substrate 12 with cathodes 11 and thesubstrate 30 with anodes 13 are sealed around a frame 15 with a vacuumthat is preferably less than 1×10⁻⁶ Torr.

[0049] The frame 15 is configured for placement between the cathodes 11and anodes 13 at the peripheries to provide standoff there between andthereby define an interspace region 17. The cathodes 11 have the fieldemission substrate 12, the conductive layer 14, the gate seed layer 16,the gate layer 18, and the emitter well 20. The bleed layer 15 over theconductive layer 14 can also be optionally included in accordance withthe present invention. The emitter well 20 contains the nano-supportedcatalyst layer 22 over the conductive layer 14, and the nanotubes 24 aregrown on the nano-supported catalyst layer 22 as previously described inthis detailed description of the drawings. The anodes 13 have thesubstrate 30 that is spaced from the gate layer 18, a transparentconductive layer 32, and a cathodoluminescent deposit 36 formed on thetransparent conductive layer 32. The interspace region 17 is evacuatedto a pressure of about 1×10⁻⁶ Torr.

[0050] The operation of FED 10 includes applying suitable potentials atthe conductive layer 14, gate layer 18 and transparent conductive layer32 for extracting electrons from selectively addressed nanotubes 24 andcausing the electrons to traverse out of the corresponding emitter wells20, across interspace region 17, to be received by cathodoluminescentdeposits 36, thereby causing them to emit light. In a preferredembodiment of the present invention, a potential of approximatelyseveral thousand volts is applied to the anodes 13. The gate 86 has twooperating modes or potentials. In a first mode, the electric fieldapplied on the anode 13 is sufficient to extract electrons from theemitters 24. To turn the device on and extract electrons, the gatepotential applies a gate field, which is about equal to or larger thanthe anode field. To turn the device off and eliminate the flow ofelectrons, the gate potential applies a field that is eithersignificantly smaller than the anode field or the opposite polarity ofthe anode field. The gate potential in the first mode produces alignmentof electron extraction electric field lines 88. Since electrons aregenerally emitted from the nanotubes 24 in a generally perpendiculardirection with respect to the conductive layer 14, only a relativelysmall amount of focusing can be used to correct for stray electrons orspreading of the beam. In a second mode, the electric field applied bythe anodes is insufficient to extract electrons from the emitters 24. Toturn the device on, a gate potential is applied to create a gate fieldsufficient to extract electrons from the electron emitters. To turn thedevice off, a smaller gate potential is applied, which is insufficientto extract electrons from the emitters 24.

[0051] The FED 10 constructed according to the present invention canhave a triode geometry from about one-tenth of a micron (0.10 μm) toabout twenty-five microns (25 μm); a gate spacing less than abouttwenty-five microns (25 μm); a switching voltage that is preferably lessthan about eighty (80) volts and more preferably less than about fifty(50) volts with a cathode current preferably greater than about one halfmilliamp per square centimeter (0.5 mA/cm²), more preferably greaterthan one and one half milliamps per square centimeter (1.5 mA/cm²); anda lifetime performance of greater than three thousand (3,000) hours. Theswitching voltage of FED 10 is dependent upon the diameter and theaspect ratio of the nanotubes 24.

[0052] It is preferable to construct the FED 10 such that the deviceswitches with the desired field emission current density at lowswitching voltages that is less than about eighty volts (80 V) and morepreferably less than about fifty volts (50 V). This provides an FED 10configuration that enables the use of low voltage driver electronics forswitching current densities of approximately one milliamp per squarecentimeter (1 mA/cm2) and also current densities that exceed one ampereper square centimeter (1 A/cm2). It is also preferable to provide theFED 10 with the low switching voltage using inexpensive deviceprocessing techniques, such as the device processing techniquesdescribed in this detailed description of the drawings, and the FED 10is also preferably designed with specific combinations of gate electrodespacing, nanotube diameter, nanotube height, and nanotube density toprovide the low switching voltage property.

[0053] The low voltage switching is typically achieved over a relativelynarrow range of combinations for the gate electrode spacing, nanotubediameter, nanotube height and nanotube density. The specificcombinations depend to some extent on the desired operating conditionsfor the FED. When the nanotubes have spacings that are approximatelyless that the height of the nanotubes, the switching field applied bythe gate electrode is screened by adjacent nanotubes and electronextraction from the nanotube is less than efficient, which results in anincreased switching voltage. This results in an undesirable increase inthe switching voltage for approximately the same current. Therefore, thelength of the nanotubes is preferably on the order of ten (10)micrometers or less in order to avoid field screening while achievingsufficient current density with about one million emitting nanotubes persquare centimeter.

[0054] The switching voltage for a given combination of device geometry,nanotube height, nanotube diameter and nanotube spacing can be predictedfrom field emission theory in combination with electric field modeling.However, the general procedure can be outlined with a simplified model,which produces results that are adequate to define the useful range ofgeometrical and nanotube dimensions for a low voltage switching. Anexample electrode geometry that illustrates the switching voltagerequirements is a cathode plate with a single protruding nanotube havinga height (h), an anode plate spaced a distance (d), which is greaterthan the height (h) from the cathode plate. Both the cathode and anodeplates extend too much greater distances in a plane perpendicular to thenanotube.

[0055] This example geometry is a simplified structure solely for thepurpose of illustrating the switching voltage and does not contain ananode electrode. However, the geometry is similar to that of thepreferred embodiment of the present invention with a gate electrodehaving an aperture at a location proximate to the nanotube, and an anodeelectrode positioned above the gate electrode. The electric fields andvoltages are similar for the simplified example and the preferredembodiment of similar dimensions. In the example geometry, the nanotubedoes not have a height greater than the spacing distance (d). However,an increase in the height of the nanotube decreases the switchingvoltage. In the preferred embodiment of the present invention having thegate electrode with the aperture, the nanotube can extend to a distance(d) and the aperture diameter is about d/2 so that the nanotube isspaced from the electrode by about d/2. Similar computational resultsare obtained in the simplified example geometry for a height (h) of d/2.Practically, it is difficult to control the geometry with a good yieldwhen the height (h) is greater than about one half (0.5) of the distance(d). Consequently, a practical geometrical configuration for thisillustrative example based on fabrication procedures is a height (h) ofd/2 with yields about equal to the lowest practical switching voltage.

[0056] The swing voltage increases with the diameter of the nanotube.For nanotubes with a diameter greater than about twelve (12) nm in theexample geometry, the switching voltage exceeds eighty volts (80 V).However, devices using nanotubes with diameters less than about fivenanometers (5 nm) nanometers can switch the desired current with avoltage that is less than about fifty volts (50 V). While a device canbe configured with a nanotube size and geometry that allows a fieldemission device to operate with a switching voltage less than eightyvolts (80 V), a nanotube diameter that is less than about twentynanometers (20 nm) would be typical for the device. More generally, thenanotube diameter for a device that switches the desired current densitywith manufacturable geometries using less than about eighty volts (80 V)has a nanotube diameter that is substantially less than about twelvenamometers (12 nm).

[0057] This example also illustrates that relationship of the nanotubeaspect ratios (i.e., nanotube height divided by nanotube diameter) for afield emission device with a low switching voltage. For example, theaspect ratio of nanotubes with about twelve nanometer (12 nm) diametersis preferably greater than about two hundred (200) for an electrodespacing of approximately five (5) micrometers, about four hundred (400)for an electrode spacing of approximately ten (10) micrometers, andabout eight hundred (800) for an electrode spacing of approximatelytwenty (20) micrometers. Likewise, the aspect ratio of nanotubes withsmaller diameters such as two nanometers (2 nm) is approximately greaterthan about twelve hundred and fifty (1250) for an electrode spacing offive (5) micrometers and about two thousand five hundred (2500) for anelectrode spacing of about ten (10) micrometers, and about five thousand(5000) for an electrode spacing of approximately twenty (20)micrometers.

[0058] As previously described in this detailed description of thedrawings, the FED 10 is preferably constructed to obtain a low switchingvoltage and preferably constructed to have a gate electrode to cathodeplane spacing ranging from about one-tenth of a micron (0.10 μm) toabout twenty-five microns (25 μm). For low cost processing, it isdesirable to use a gate electrode to cathode plane spacing rangingbetween about five microns (5 μm) to about twenty-five microns (25 μm).In a most preferred embodiment of the present invention, it is desirableto construct the FED 10 with about a ten (10) micrometer gate to cathodespacing, incorporating greater than one million emitting nanotubes persquare centimeter of cathode area with the emitting nanotubes havingdiameters of approximately two nanometers (2 nm) to five nanometers (5nm), heights of approximately three (3) to five (5) micrometers, and thespacing between emitting nanotubes at least approximately three (3) tofive (5) micrometers. These conditions are sufficient to switch morethan 1 mA/cm2 of current with less than 80 V.

[0059] From the foregoing description, it should be appreciated a lowgate voltage FED and methods of forming a low gate voltage FED areprovided with present significant benefits, which are described in thebackground of the invention and the detailed description of preferredexemplary embodiments, and also would be apparent to one skilled in theart. Furthermore, while preferred exemplary embodiments have beenpresented in the foregoing description of preferred exemplaryembodiments, it should be appreciated that a vast number of variationsin the embodiments exist. Lastly, it should be appreciated that theseembodiments are preferred exemplary embodiments only, and are notintended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the foregoing detailed descriptionprovides those skilled in the art with a convenient road map forimplementing a preferred exemplary embodiment of the invention. It beingunderstood that various changes may be made in the function andarrangement of elements described in the exemplary preferred embodimentswithout departing from the spirit and scope of the invention as setforth in the appended claims.

APPENDIX I EXAMPLE I

[0060] 1. Immerse a borosilicate glass with a copper (Cu) metal pattern(i.e., substrate with an electrode) into a solution of 1×10⁻²M Al(NO₃)₃in isopropyl alcohol (IPA) and apply a negative twenty volt (−20V) biasto the copper metal pattern while keeping a counter electrode, which canbe constructed out of stainless steel, at ground for a duration of one(1) minute. The desired chemical reactions involved in this step are:

[0061] Al(NO₃)₃ Al(NO₃)²⁺+NO₃ occurring in the solution;

[0062] Al(NO₃)₂ ⁺+30H⁻→Al(OH)₃+2NO₃ ⁻occurring at the electrode; and

[0063] Al(OH)₃ is the solid partial nano-supported catalyst that isforming at the electrode.

[0064] 2. Dry the borosilicate glass with the copper metal pattern withthe partially formed nano-supported catalyst with a fifteen (15) minutebake at eighty degrees Celsius (80° C.)

[0065] 3. Immerse the borosilicate glass with the copper metal patternwith the partially formed nano-supported catalyst into a solution of1×10⁻³ Fe(NO₃)₃·9H₂O M (iron(III)nitrate hydrate) in IPA and apply anegative five volt (−5V) bias to the copper metal pattern while keepinga counter electrode at ground for a duration of about one (1) minute.The desired chemical reactions involved in this step are:

[0066] Fe(NO₃)₃→Fe(NO₃)₂ ⁺+NO₃ ⁻occurring in solution;

[0067] Fe(NO₃)⁺+30H⁻→Fe(OH)₃+2NO₃ ⁻and Fe(NO₃)⁺²+30H⁻→Fe(OH)₃+NO₃⁻occurring at the electrode; and

[0068] Fe(OH)₃ is the solid partial nano-supported catalyst that isforming at the electrode.

[0069] 4. Dry the borosilicate glass with the copper metal patternhaving the nano-supported catalyst formed of Al₂O₃/FeO_(x) with afifteen (15) minute bake at eighty degrees Celsius (80° C.).

[0070] 5. Perform hot filament chemical vapor deposition (HFCVD) growthat five hundred and eighty degrees Celsius (580° C.) with rheniumfilament, and a gas mixture of methane (CH₄) and hydrogen (H₂) at a fourto one ratio for thirty (30) minutes.

[0071] 6. The resulting carbon nanotube layer can be best described as atangled carpet of carbon nanotubes with diameters on the order of aboutone nanometer (1 nm) to about three nanometers (3 nm) and an aspectratio of ranging from one thousand (1,000) to 2,000).

EXAMPLE II

[0072] 1. Immerse a borosilicate glass with a copper (Cu) metal pattern(substrate with an electrode) into a solution with 1×10⁻²M Mg(NO₃)₂ inisopropyl alcohol (IPA) and apply negative twenty volts (−20V) to thecopper metal pattern while keeping a counter electrode, which can beconstructed out of stainless steel, at ground for a duration of one (1)minute. The desired chemical reactions involved in this step are:

[0073] Mg(NO₃)₂→Mg(NO₃)⁺+NO₃ ⁻occurring in the solution;

[0074] Mg(NO₃)⁺+2OH⁻→Mg(OH)₂+NO₃ ⁻occurring at the electrode; and

[0075] Mg(OH)₂ is the solid partial nano-supported catalyst that isforming at the electrode.

[0076] 2. Dry the borosilicate glass with the copper metal patternhaving the partially formed nano-supported catalyst with a fifteen (15)minute bake at eighty degrees Celsius (80° C.)

[0077] 3. Immerse the borosilicate glass with the copper metal patternhaving the partially formed nano-supported catalyst into a solution of1×10⁻³ Fe(NO₃)₃·9H₂O M (iron(III)nitrate hydrate) in IPA and apply anegative five volt (−5V) bias to the copper metal pattern while keepinga counter electrode at ground for a duration of one (1) minute. Thedesired chemical reactions involved in this step are:

[0078] Fe(NO₃)₃→Fe(NO₃)₂ ⁺+NO₃ ⁻occurring in solution;

[0079] Fe(NO₃)⁺+3OH⁻→Fe(OH)₃+2NO₃ ⁻and Fe(NO₃)⁺²+3OH⁻→Fe(OH)₃+NO₃⁻occurring at the electrode; and

[0080] Fe(OH)₃ is the solid partial nano-supported catalyst that isforming at the electrode.

[0081] 4. Dry the borosilicate glass with the copper metal pattern withthe formed nano-supported catalyst of Mg₂O₂/FeO_(x) with a fifteen (15)minute bake at eighty degrees Celsius (80° C.).

[0082] 5. Perform hot filament chemical vapor deposition (HFCVD) growthat six hundred degrees Celsius (600° C.) with rhenium filament, and agas mixture of methane (CH₄) and hydrogen (H₂) at a four to one ratiofor thirty (30) minutes.

EXAMPLE III

[0083] 1. Immerse a borosilicate glass with a copper metal pattern(substrate with an electrode) into a solution with 1×10⁻²M Al(NO₃)₃ plus1×10⁻³ Fe(NO₃)₃·9H₂O M in isopropyl alcohol (IPA) and apply a negativeten volt (−10V) bias to the copper metal pattern while keeping a counterelectrode, which can be constructed out of stainless steel, at groundfor a duration of one (1) minute. The desired chemical reactionsinvolved in this step are:

[0084] Al(NO₃)₃→Al(NO₃)²⁺+NO₃ ⁻and Fe(NO₃)₃→Fe(NO₃)₂ ⁺+NO₃ ⁻occurring inthe solution;

[0085] Al(NO₃)₂ ⁺+3OH⁻→Al(OH)₃+2NO₃ ⁻, Fe(NO₃)⁺ +3OH ^(−→Fe(OH)) ₃+2NO₃⁻and Fe(NO₃)⁺²+3OH⁻→Fe(OH)₃+NO₃ ⁻occurring at the electrode; and Al(OH)₃and Fe(OH)₃ are the solid nano-supported catalyst that is forming at theelectrode.

[0086] 2. Dry the borosilicate glass with the copper metal pattern withthe formed nano-supported catalyst of Al₂O₃/FeO_(x) with a fifteen (15)minute bake at eighty degrees Celsius (80° C.).

[0087] 3. Perform hot filament chemical vapor deposition (HFCVD) growthat six hundred degrees Celsius (600° C.) with rhenium filament, and agas mixture of methane (CH₄) and hydrogen (H₂) at a four to one ratiofor thirty (30) minutes.

EXAMPLE IV

[0088] 1 . Individual nickel and aluminum sources, both are 99.9% pure,are deposited through a polymer mask (i.e., PMMA) by electron-beamco-evaporation onto molybdenum photo-resist patterned substrate (i.e.borosilicate glass with a molybdenum electrode) to form an one hundredand fifty nanometers (150 nm) thick patterned mixed metal alloy layerconsisting of fifty percent (50%) nickel and fifty percent (50%)aluminum onto substrate.

[0089] 2. The photo-resist on the substrate is removed by dissolution inacetone and the mixed metal alloy layer of the prescribed patternremained on the substrate.

[0090] 3. The substrate with the patterned mixed alloy layer is immersedfor five (5) minutes into a solution containing NH₄OH, H₂O₂, and H₂O inthe ratio of one to one to five (1:1:5) respectively at a temperature offorty Celsius (40° C.) with the desired chemical reaction ofAl+3NH₄OH→Al(OH)₃+NH₄ ⁺occurring in the mixed metal alloy film to form aNi—Al nano-supported sponge catalyst. The Al(OH)₃ is the metal oxidenano-support structural element of the Ni—Al nano-supported spongecatalyst.

[0091] 4. Dry the substrate with the patterned Ni—Al nano-supportedsponge catalyst by baking it at eighty degree Celsius (80° C.) forfifteen (15) minutes.

[0092] 5. Perform hot filament chemical vapor deposition (HFCVD) growthat five hundred and eighty degrees Celsius (580° C.) with rheniumfilament, and a gas mixture of methane (CH₄) and hydrogen (H₂) at a fourto one ratio for thirty (30) minutes.

EXAMPLE V

[0093] 1. Prepare a nanocatalyst solution containing 0.1 gramsFe(N03)3.9H20, 0.03 grams of molybdenyl acetylacetonate, 75 ml water,and 0.75 of nanoparticle alumina or silica that is mixed for abouttwenty four hours and sonicated for about one hour.

[0094] 2. Prepare a borosilicate glass substrate with metallization anda removable photo patterned layer that contains openings at desirednanotube locations.

[0095] 3. Disperse the nanocatalyst solution onto the photo patternedlayer and dry the solution at eighty-five degrees Celsius.

[0096] 4. Conduct the formation of the field emission device structure.

[0097] 5. Perform hot filament chemical vapor deposition (HFCVD) growthat five hundred and eight degrees Celsius with a rhenium filament and agas mixture of methane and hydrogen at a four to one ratio forapproximately thirty minutes.

What is claimed is:
 1. A field emission device, comprising: a substratehaving a deformation temperature that is less than about six hundred andfifty degrees Celsius; a nano-supported catalyst formed on saidsubstrate, said nano-supported catalyst having active catalyticparticles that are less than about five hundred nanometers; and ananotube that is catalytically formed in situ on said nano-supportedcatalyst, said nanotube having a diameter that is less than about twentynanometers.
 2. The field emission device of claim 1, wherein saidnanotube with said diameter that is less than about twenty nanometers isconfigured to provide a switching voltage that is less than about eightyvolts.
 3. The field emission device of claim 1, wherein a currentdensity drawn from said field emission device is greater than aboutone-half milliamp per squared centimeter.
 4. The field emission deviceof claim 1, wherein said nanotube that is catalytically formed in situon said nano-supported catalyst is catalytically formed in situ on saidnano-supported catalyst with hot filament chemical vapor deposition(HFCVD).
 5. The field emission device of claim 2, wherein said switchingvoltage is less than about fifty volts.
 6. The field emission device ofclaim 1, wherein said active catalytic particles are less than aboutfifty nanometers.
 7. The field emission device of claim 1, wherein saiddiameter of said nanotube is less than about five nanometers.
 8. Thefield emission device of claim 1, wherein said nanotube has an aspectratio of greater than approximately one hundred and forty and less thanapproximately four thousand and five hundred.
 9. The field emissiondevice of claim 1, wherein said nanotube is single-wall nanotube. 10.The field emission device of claim 1, wherein said nanotube ismulti-wall nanotube.
 11. The field emission device of claim 3, whereinsaid current density drawn from said field emission device is greaterthan about one and one-half milliamp per squared centimeter.
 12. Thefield emission device of claim 1, wherein said substrate comprises atleast one material selected from the group consisting of borosilicateglass, sodalime glass, carbon, silicon, ceramics, metals, and compositematerials.
 13. The field emission device of claim 1, wherein said fieldemission device is configured to provide a gate spacing of less thanabout twenty-five microns.
 14. The field emission device of claim 1,further comprising an anode.
 15. The field emission device of claim 14,wherein a second distance between said anode and said substrate isgreater than about two hundred and fifty microns and less than aboutfive thousand microns.
 16. The field emission device of claim 1, whereina thickness of said nano-supported catalyst is less than one micron. 17.The field emission device of claim 1, wherein said nano-supportedcatalyst is comprised of said active catalytic particles that areselected from the group consisting of iron, nickel, cobalt and a metaloxide selected from the group consisting of alumina, silica andmagnesium oxide.
 18. The field emission device of claim 1, wherein saidnano-supported catalyst is comprised of: a porous sub-layer having saidactive catalytic particles supported by a metal oxide structure; and anon-porous sub-layer having said active catalytic particles and astructural metallic element.
 19. The firld emission device of claim 18,wherein said porous sub-layer has a surface area to volume ratio ofgreater than about fifty meter square per gram (50 m²/g).
 20. A methodof forming a field emission device comprising: providing a substratehaving a deformation temperature that is less than about six hundred andfifty degrees Celsius; forming a nano-supported catalyst on saidsubstrate, said nano-supported catalyst having active catalyticparticles that are less than about five hundred nanometers; andconducting a chemical reaction process to grow a nanotube on saidnano-supported catalyst, said nanotube having a diameter that is lessthan about twenty nanometers.
 21. The method of forming the fieldemission device of claim 20, wherein said field emission device isconfigured to provide a switching voltage that is less than about eightyvolts with a current density drawn from said field emission device thatis greater than about one-half milliamp per squared centimeter.
 22. Themethod of forming the field emission device of claim 20, wherein saidchemical reaction process is comprised of a hot filament chemical vapordeposition (HFCVD).
 23. The method of forming the field emission deviceof claim 20, further comprising of depositing a bleed layer ofconductive material.
 24. The method of forming the field emission deviceof claim 17, wherein said forming said nano-supported catalyst on saidsubstrate is comprised of: immersing said substrate into a solventcontaining a first metal salt and a second metal salt; and applying abias voltage to said electrode such that said nano-supported catalyst isat least partly formed with said first metal salt and said second metalsalt on said substrate.
 25. The method of forming the field emissiondevice of claim 24, wherein said first metal salt is selected from thegroup consisting of aluminum nitrate, magnesium nitrate, calcium nitrateor combination thereof.
 26. The method of forming the field emissiondevice of claim 24, wherein said active catalytic particles are derivedfrom said second metal salt and are selected from the group consistingof iron, nickel, cobalt, ruthenium, rhodium, palladium, rhenium, osmium,iridium and platinum.
 27. The method of forming the field emissiondevice of claim 20, wherein said forming said nano-supported catalyst onsaid substrate is comprised of: immersing said substrate into a firstsolvent containing a first metal salt; applying a first bias voltagesuch that said nano-supported catalyst is at least partly formed withsaid first metal salt on said substrate; removing said substrate fromsaid first solvent containing said first metal salt; immersing saidsubstrate into a second solvent containing a second metal salt; andapplying a second bias voltage in said second solvent such that saidnano-supported catalyst is partly formed with said second metal salt.28. The method of forming the field emission device of claim 27, whereinsaid first metal salt is selected from the group consisting of aluminumnitrate, magnesium nitrate and calcium nitrate.
 29. The method offorming the field emission device od claim 27, wherein said activecatalytic particles are derived from said second metal salt, which isselected from the group consisting of iron, nickel, cobalt, ruthenium,rhodium, palladium, rhenium, osmium, iridium and platinum.
 30. Themethod of forming the field emission device of claim 20, wherein saidforming said nano-supported catalyst is comprised of: depositing anactive catalytic metallic element on said substrate; depositing astructural metallic element with said active catalytic metallic elementto form a mixed metal alloy layer on substrate; and etching said mixedmetal alloy layer with an etchant to oxidize said active catalyticmetallic element and said structural metallic element and to remove atleast a portion of said structural metallic element from a firstsub-layer of said mixed metal alloy layer, wherein said first sub-layerof said mixed metal layer is porous and comprised of said activecatalytic particles of said active catalytic metallic element andsupported by a metal oxide structure derived from the structuralmetallic element, and said mixed metal alloy layer other than said firstsub-layer and said first sub-layer form the nano-supported catalyst onsaid substrate.
 31. The method of forming the field emission device ofclaim 30, wherein said active catalytic metallic element and saidstructural metallic element have different electrochemical selectivityso as to allow said etchant to remove at least a portion of saidstructural metallic element from a first sub-layer of said mixed metalalloy layer.
 32. The method of forming the field emission device ofclaim 30, wherein said depositing said active catalytic metallic elementon said substrate and said depositing said structural metallic elementwith said active catalytic metallic element to form said mixed metalalloy layer on said substrate is accomplished with a coevaporationdeposition.
 33. The method of forming the field emission device of claim30, wherein said active catalytic metallic element is selected from thegroup consisting of titanium, vanadium, chromium, manganese, copper,zirconium, niobium, molybdenum, silver, hafnium, tantalum, tungsten,rhenium, gold, ruthenium, rhodium, palladium, osmium, iridium, platinum,iron, cobalt and nickel.
 34. The method of forming the field emissiondevice claim 30, wherein said structural metallic element is selectedfrom the group consisting of aluminum, silicon and magnesium.
 35. Themethod of forming the field emission device claim 30, further comprisingadding a catalytic promoter as a ternary element.
 36. The method offorming the field emission device of claim 31, wherein said ternaryelement is selected from the group of consisting of calcium, tantalum,hafnium and zirconium.
 37. The method of forming the field emissiondevice claim 30, wherein said etchant is selected from a groupconsisting of ammonium hydroxide solution, an alkaline solution, anitric acid solution, a hydrochloric acid solution, and an acidicsolution.
 38. The method of claim 20, further comprising forming a gatehaving an aperture.
 39. The method of claim 38, wherein forming saidgate having said aperture is comprised of: forming a sacrificial layerof material surrounding said nano-supported catalyst, said sacrificiallayer having a depth and width that defines a gate separation from saidnano-supported catalyst; forming a gate seed layer on said sacrificiallayer; forming a first mask on said gate seed layer, said first maskdefining said gate aperture and gate edges; depositing a gate layer onsaid gate seed layer using said first mask, said gate layer and saidgate seed layer combining to form said gate; removing said first mask;etching an opening through said gate seed layer using said gate layer asa second mask; and removing said sacrificial layer surrounding saidlayer of nano-supported catalyst.